Human Body Systems

Human Body Systems Animal organs are usually composed of more than one cell type. Organs perform a certain function. Most organs have functions in only one organ system. Organ systems are composed of organs, and perform a major function for the organism. Digestive System Multicellular organisms need to digest their food and filter the waste and the nutrients. The digestive system uses mechanical and chemical methods to break food down into nutrient molecules that can be absorbed into the blood. There are a few steps commonly involved to correctly digest: 1. movement: propels food through the digestive system 2. secretion: release of digestive juices in response to a specific stimulus 3. digestion: breakdown of food into molecular components small enough to cross the plasma membrane 4. absorption: passage of the molecules into the body's interior and their passage throughout the body 5. elimination: removal of undigested food and wastes Circulatory System Multicellular animals do not have most of their cells in contact with the external environment and so have developed circulatory systems to transport nutrients, oxygen, carbon dioxide and metabolic wastes. Components of the circulatory system include •

blood: a connective tissue of liquid plasma and cells • heart: a muscular pump to move the blood • blood vessels: arteries, capillaries and veins that deliver blood to all tissues Respiratory System The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood. Among four-legged animals, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange

takes place. A diaphragm pulls air in and pushes it out. Respiratory systems of various types are found in a wide variety of organisms. Even trees have respiratory systems. The Nervous System

The Endocrine System The endocrine system is a collection of glands that secrete chemical messages we call hormones. These signals are passed through the blood to arrive at a target organ, which has cells possessing the appropriate receptor. Exocrine glands (not part of the endocrine system) secrete products that are passed outside the body. Sweat glands, salivary glands, and digestive glands are examples of exocrine glands. Hormone Adrenocorticotropi c Growth hormone Follicle-stimulating hormone Luteinizing hormone Prolactin Thyroidstimulating hormone Melanocytestimulating hormone Antidiuretic hormone Oxytocin

Gland Origin Pituitary gland (anterior) Pituitary gland (anterior) Pituitary gland (anterior) Pituitary gland (anterior) Pituitary gland (anterior) Pituitary gland (anterior) Pituitary gland (anterior) Pituitary gland (posterior) Pituitary gland

Target Tissue

Function

Adrenal cortex

Triggers secretion of hydrocortisone from the adrenal gland

Throughout body

Stimulates growth and development

Sex glands

Stimulates female egg maturation and male sperm production

Sex glands

Stimulates female ovulation and male secretion of testosterone

Mammary glands

Stimulates milk production in the breasts after childbirth

Thyroid gland

Triggers secretion of thyroid hormones

Melanin-producing cells

Controls skin pigmentation

Kidneys

Regulates water retention and blood pressure

Uterus

Triggers contraction of the uterus during labor

(posterior)

Mammary glands

Melatonin

Pineal gland

Calcitonin

Thyroid gland Thyroid gland

Unclear, although possible target sites are pigment cells and sex organs Bones

Thyroid hormone

Throughout body

Parathyroid hormone Thymosin

Parathyroid glands Thymus

Bones, intestines, and kidneys White blood cells

Aldosterone

Adrenal gland Adrenal gland

Kidneys

Epinephrine

Adrenal gland

Muscles and blood vessels

Norepinephrine Glucagon

Adrenal gland Pancreas

Muscles and blood vessels Liver

Insulin

Pancreas

Throughout body

Estrogen

Ovaries

Female reproductive system

Progesterone

Ovaries

Testosterone

Testes

Mammary glands Uterus Throughout body

Erythropoietin

Kidney

Bone Marrow

Hydrocortisone

Throughout body

Stimulates milk letdown for breastfeeding after childbirth May affect skin pigmentation; may regulate biorhythms (awake/sleep patterns) and prevent jet lag Controls the level of calcium in the blood by depositing it in the bones Increases the body's metabolic rate; promotes normal growth and development Regulates calcium level in blood Promotes the growth and development of white blood cells, helping the body fight infection Regulates sodium and potassium levels in the blood to control blood pressure Plays key role in stress response; increases blood glucose levels and mobilizes fat stores; reduces inflammatation Increases blood pressure, heart and metabolic rate, and blood sugar levels; dilates blood vessels. Also released during exercise Increases blood pressure and heart rate; constricts blood vessels Stimulates the breakdown of glycogen (stored carbohydrate) into glucose (blood sugar); regulates glucose blood level Regulates blood glucose levels; increases storage of glycogen; facilitates glucose intake by body cells Causes sexual development and growth; maintains proper functioning of female reproductive system Prepares uterus for pregnancy Causes sexual development and growth spurt; maintains proper functioning of male reproductive system Produces red blood cells

A reflex is an involuntary, or automatic, action that your body does in response to something - without you even having to think about it. You don't decide to kick your leg, it just kicks. There are many types of reflexes and every healthy person has them. In fact, we're born with most of them. Reflexes protect your body from things that can harm it. For example, if you put your hand on a hot stove, a reflex causes you to immediately remove your hand before the message, "Hey, this is hot!" even gets to your brain. The three types of neurons are arranged in circuits and networks, the simplest of which is the reflex arc.

In a simple reflex arc, such as the knee jerk, a stimulus is detected by a receptor cell, which synapses with a sensory neuron. The sensory neuron carries the impulse from site of the stimulus to the central nervous system (the brain or spinal cord), where it synapses with an interneuron. The interneuron synapses with a motor neuron, which carries the nerve impulse out to an effector, such as a muscle, which responds by contracting.